Problem: $\cos(-1\pi) = \text{?}$
Answer: To find the cosine using the unit circle, first find the angle. Drag the orange point around the circle until $-1\pi$ is selected. The correct angle is selected. Remember, the cosine of an angle is represented by the $x$ coordinate of a point on the unit circle. The $x$ coordinate of the point is $-1$, so $\cos(-1\pi) = -1$.